Magnetoencephalography (MEG) will be used to detect and characterize focal abnormalities in neurophysiological function in subjects with MTBI diagnosed with PTSD for the purpose of distinguishing between the two. MEG is a completely non-invasive imaging modality which is able to provide information regarding focal abnormalities in the brain. MEG has been shown to be sensitive to cognitive complaints in patients with MTBI and to be more sensitive to these deficits than EEG. In addition, neurophysiological abnormalities found through testing can differentiate patients with MTBI and PTSD in some studies. Thus, we propose to explore the relationship between DTI and MEG findings which may lead to identification of more distinct, replicable patterns of brain abnormalities in subjects with PTSD and MTBI that may lead to better differentiation between these groups of patients and improve diagnostic precision, as well as from patients with a combination of both disorders.